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Ultra-Compact Wideband Electro-Optic Modulator based on Ferroelectric Materials


OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Microelectronics; Quantum Science; Space Technology; Advanced Materials OBJECTIVE: Develop a new ultra-compact, wideband, electro-optic modulator by exploiting ferroelectric materials for the purpose of radio frequency (RF) photonic link applications in DoD platforms. DESCRIPTION: The replacement of the coaxial cable used in various onboard RF/analog applications with RF/analog fiber optic links requires ruggedized, high dynamic range and wideband electro-optic modulators. Current military communications and electronic warfare systems require ever increasing bandwidths while simultaneously requiring reductions in size, weight and power (SWaP). Replacement of the coaxial cabling would provide increased immunity to electromagnetic interference, reduction in size and weight, and an increase in bandwidth and power, however it requires an innovative modulator to complete the system. The ability to harness and control the electro-optic effect in a sub-micron-thick film of a ferroelectric could revolutionize optical switches used in Si photonics. To fully realize the tremendous potential of this novel concept, ferroelectric materials on silicon, which have the largest electro-optic coefficients known for a low loss material, show promise. Recent advances in film growth methods that allow for fabrication of ferroelectric transition metal oxides directly on Si created ground-breaking opportunities in silicon photonics, a hybrid technology combining semiconductor logic with optical information technologies. The desired electro-optic modulators used in RF/analog fiber optic links must be compatible with distributed feedback (DFB) lasers with greater than 100 mWatts of single-mode fiber coupled optical power. These modulators in the future might have dual outputs for use with balanced photo detector receivers which would enable a higher link gain, a lower noise figure and a higher spur free dynamic range, as required in DoD systems. A minimum 3 dB optical bandwidth of up to 40 GHz is required, with V-pi less than 5V at 40GHz and below, and it must be compatible with emerging systems out to 100 GHz. A twofold reduction in SWaP requirements as compared to current electro-optic modulators must be achieved without any degradation in device performance. A future major challenge that must be analyzed is to develop a new compact modulator packaging approach that can achieve operation over a minimum temperature range of -40 to +120 degrees Celsius to avoid material specific phase transition, this will likely require active temperature controls to operate. This key criterion must be met without sacrificing modulator bandwidth and drive voltage efficiency, while demonstrating low optical insertion loss at fiber-coupled DFB laser powers up to 200 mWatts, and possibly higher in the future. PHASE I: Develop a ferroelectric on silicon modulator fabrication process, demonstrate feasibility of the modulator with a supporting proof of principle bench top experiment, and analyze electro-optic modulator performance to meet the target metrics identified above. PHASE II: Optimize the growth and processing techniques required for the modulator fabrication. Initially the modulators will likely be stand-alone devices but by the end of phase II a roadmap must be developed for transition to heterogeneous fabrication of integrated systems. At the end of phase II demonstration of greater than 2 square centimeters of high-quality single domain ferroelectric material must be attained, along with a demonstration of reliable fabrication processes for either fiber coupled or integrated modulators exceeding 3dB optical bandwidth at frequency 40GHz or higher and identification most pertinent direction and use of optical coefficients, i.e., r33 or r42. PHASE III DUAL USE APPLICATIONS: Perform extensive modulator reliability and durability testing. Develop packaging for both stand alone and integrated systems. Transition the demonstrated technology to Air platforms and interested commercial applications. The technology would find application in commercial systems such as fiber optic networks and telecommunications. REFERENCES: 1. A. Rahim, A. Hermans, B. Wohlfeil, D. Petousi, B. Kuyken, D. Van Thourhout and R. Baetsa, “Taking silicon photonics modulators to a higher performance level: state-of-the-art and a review of new technologies,” Adv. Photonics 3, 024003 (2021); 2. S. Abel, F. Eltes, J. E. Ortmann, A. Messner, P. Castera, T. Wagner, D. Urbonas, A. Rosa, A. M. Gutierrez, D. Tulli, P. Ma, B. Baeuerle, A. Josten, W. Heni, D. Caimi, A. A. Demkov, J. Leuthold, P. Sanchis and J. Fompeyrine, “Large Pockels effect in micro- and nano-structured barium titanate integrated on silicon,” Nature Materials 18, 42 (2019); 3. C. Xiong, W. H. P. Pernice, J. H. Ngai, J. W. Reiner, D. Kumah, F. J. Walker, C. H. Ahn, and H. X. Tang, "Active Silicon Integrated Nanophotonics: Ferroelectric BaTiO3 Devices," Nano Letters 14, 1419 (2014). KEYWORDS: Ultra-Wideband; Electro-Optic Modulator; Dual-Output; Extended Temperature Range; Analog Fiber Optic Links
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